We propose to examine two questions which relate to the regulation of brain extracellular fluid acid-base balance. First, is carbonic anhydrase important to this regulatory mechanism? We will examine this questions in the isolated spinal cord, a segment of central nervous system devoid of the influence of choroid plexus. Methazolamide, a specific carbonic anhydrase inhibitor, will be introduced into the spinal fluid in a mock spinal fluid perfusate. The clearance and distribution of the drug in spinal fluid and spinal cord tissue will be determined using an assay for methazolamide. A carbonic anhydrase inhibition regimen will be developed which will allow us to examine spinal fluid (H ion) regulation under conditions of steady-state enzyme inhibition. The second questions is: Does CSF (H ion) regulation take place at, or require an intact, parenchymal capillary blood-brain barrier? We will open the tight junctions, which seal the interspace between brain capillary endothelial cells, by osmotic shock or by brief, severe hypertension. Then acute acid-base disturbances will be imposed and the degree of regulation of CSF (H ion) with intact and with "opened" blood-brain barrier will be compared.